1. Field of the Invention
Aspects of the present invention relate to an atomic layer deposition apparatus and a method of fabricating an atomic layer using the same. More particularly, aspects of the present invention relate to an atomic layer deposition apparatus and a method of fabricating an atomic layer using the same by which deformation of a substrate due to an inner temperature of a chamber during an atomic layer deposition process is prevented such that the atomic layer is uniformly formed on the substrate.
2. Description of the Related Art
Flat panel display devices are used as display devices and replace cathode ray tube display devices due to their lightweight and compact characteristics. Typical examples of such flat panel display devices are a liquid crystal display device (LCD) and an organic light emitting diode (OLED) display device. Among these, the OLED display device has advantages of better brightness and viewing angle characteristics than the LCD and a super-slim structure due to the absence of a backlight unit.
OLED display devices may be classified into a passive matrix OLED display device and an active matrix OLED display device depending on the driving method. The active matrix OLED display device has a circuit in which a thin film transistor (TFT) is used. The passive matrix OLED display device can be readily fabricated because its display region is formed as a matrix device constituted by positive and negative electrodes. However, the passive matrix OLED display device is limited to applications of low resolution and small-sized display devices due to its resolution, increase in drive voltage, decrease in lifespan of material, etc. The active matrix OLED display device has a display region in which a thin film transistor is formed on each pixel, so that uniform current can be supplied to each pixel to provide stable brightness. In addition, the active matrix OLED display device consumes less power and is suitable for providing high-resolution and large-sized display devices.
The TFT generally includes a semiconductor layer having a source region, a drain region and a channel region, a gate electrode, and source and drain electrodes. While the semiconductor layer may be formed of polycrystalline silicon (poly-Si) or amorphous silicon (a-Si), since electron mobility of the poly-Si is higher than that of the a-Si, the poly-Si is being widely used.
Methods of crystallizing the a-Si into the poly-Si may include solid phase crystallization (SPC), laser crystallization, super grain silicon (SGS) crystallization, metal induced crystallization (MIC), and metal induced lateral crystallization (MILC). The solid phase crystallization method has disadvantages in that a process time is too long and annealing at a high temperature for a long time readily causes deformation of a substrate. The laser crystallization method has disadvantages in that an expensive laser apparatus is needed and protrusions may be generated from the surface of the crystallized poly-Si to deteriorate the interface characteristics between a semiconductor layer and a gate insulating layer.
In order to overcome the disadvantages of the SPC and the laser crystallization methods, crystallization methods using metal, such as MIC, MILC, or SGS crystallization methods, which are capable of performing crystallization at a lower temperature for a shorter time than the SPC method, are used. The crystallization method using metal may include a sputtering process of applying plasma to a metal target to deposit a metal catalyst on a substrate, or an atomic layer deposition (ALD) process of forming an atomic layer of a metal catalyst on a substrate through a chemical method using a reaction gas including the metal catalyst.
However, the sputtering process has a problem in that a metal catalyst cannot be readily deposited on a substrate at an ultimately low concentration. The ALD process has a problem in that it is difficult to uniformly form an atomic layer on a substrate. In the ALD process, when a mask assembly having a plurality of holes is used to improve the uniformity of the atomic layer, the mask assembly may become deformed due to heat in a chamber required for a chemical reaction of a reaction gas during the ALD, or the reaction gas may cause a chemical reaction at the surface of the mask assembly or in the holes of the mask assembly to decrease the efficiency thereof.